Liquid crystal displays (LCDs) are widely available as flat panel displays. Recently organic light emitting diodes (OLEDs) have drawn attention as devices which can have high luminance and full color display.
Organic light emitting display devices include organic light emitting diodes including a hole injection electrode and an organic emission layer, and an electron injection electrode. Each organic light emitting diode emits light by energy generated when exciton produced by binding electrons and holes in the organic emission layer falls from the exited state into the ground state, and the organic light emitting diode (OLED) display displays the predetermined image by using the light emitting. For example, in order to provide a pixelated organic light emitting diode (OLED) display such as a television, a computer monitor, a mobile phone display, or a digital camera display, each organic light emitting diode may be arranged as a pixel having a matrix format. The pixels may be fabricated to emit the same color, so as to provide a monocolor display device; or the pixels may be fabricated to emit various different colors, for example to provide a red, green, and blue display device. The organic light emitting diode is self light emitting type, so a backlight unit for emitting light is not required unlike a liquid crystal display (LCD). Thereby, the thickness and the weight thereof may be reduced to a level of about 30% of the liquid crystal display.
Polyimide resins have received attention as an insulation layer material for the organic light emitting display device. Polyimide resins can have excellent heat resistance and stability at processes conducted at a temperature above 200° C., excellent mechanical strength, and a low dielectric constant (low-k). Polyimide resins can also provide smooth coating surfaces, lower the amount of impurities, which may deteriorate the reliability of device, and easily provide a fine pattern.
The conventional method of manufacturing an insulation layer or a semiconductor protective layer of an organic light emitting display device using the polyimide includes an additional photoresist process including, for example, etching with an organic solvent after patterning. Thus, the process is complicated; the cost is increased; the environment is contaminated by using the organic solvent; and the resist pattern may be swelled. In order to solve these problems, a negative photosensitive polyimide in which the etching solution is substituted with an alkali aqueous solution has been researched. However, in this case, the patterning can be deteriorated by non-crosslinked residue in the exposed region during the development, so that it can be difficult to achieve high resolution. Therefore, there is a need to develop a positive photosensitive polyimide which may achieve high-resolution.
Positive photosensitive resin compositions can have advantages such as providing a high contrast between the exposure part and non-exposed part by the interaction of novolac resin and a photo-sensitive agent. Heat resistance, however, is relatively low, so the pattern maintaining performance may be too decreased to ensure reliability.
In order to solve these problems, novolac resin can be mixed with polyamic acid or a polyamic acid-polyimide copolymer or the like and associated with a photo-sensitive agent of diazonaphtoquinone. It can still be difficult, however, to achieve high resolution and high sensitivity since the dissolubility difference of between an exposed region and non-exposed region is not controlled.
Accordingly, there is still a need for a positive photosensitive resin composition that can provide easy control of the dissolubility to the alkali aqueous solution of an exposed region and non-exposed region and that can provide excellent chemical resistance and heat resistance and high sensitivity.